Generally speaking, the measurement of reflectance or fluorescence or Raman signals plays a great role in biomedical applications, for example for the early diagnosis of disease-specific changes on the molecular level.
Reflectance spectroscopy is an analysis of a light reflected from tissue. Tissue reflectance spectroscopy can be used to derive information about molecules that absorbs light strongly, e.g. tissue chromophores. It can also be used to derive information about tissue scatterers, such as the size distribution of cell nucleus and average cell density.
Fluorescence spectroscopy is the analysis of fluorescence emission from tissue. Native tissue fluorophores (molecules that emit fluorescence when excited by appropriate wavelengths of light) can be sensitive to chemical composition and chemical environment changes associated with disease transformation.
Raman spectra convey specific information about the vibrational, stretching, and breathing bond energies of an illuminated sample. Raman spectroscopy probes molecular vibrations and gives very specific, fingerprint-like spectral features and has high accuracy for differentiation of malignant tissues from benign tissues. Raman spectroscopy can also be used to identify the structural and compositional differences on proteins and genetic materials between malignant tissues, their pre-cursers, and normal tissues. Naturally the Raman signal is very weak comparable to the reflectance or the fluorescence signal. In addition, the weak Raman signal can be further impeded by the interference from tissue fluorescence, and spectral contamination caused by the background Raman and fluorescence signals generated in fibers transmitting illumination light and/or spectral signals.